De-vaporizing compressed air



A ril 13; 1937. 1 s. E. "r. EWING-El AL 2,077,315

DE-VAPORIZING COMPRESSED AIR Filed April 6, 1934, 3 Sheets-Sheet 1 April13, 1937. s. E. 'r. EWING Er AL 1 DE-VAPORIZING' COMPRESSED AIR 4 FiledApril 6, 1954 3 Shee'ts-Sheet 2 IT Elvin! INYENTGRS April 13, 1937. sIEW|NG -r 2,077,315

DE-VAPORIZING COMPRESSED AIR Filed April 6, 1934 3 Sheets$heet 5 WwW ENTRS Patented 13, 1937 PATENT OFFICE- 2,071,315 nn-vsromzmc oommisssn-smSydney Edward Thacher Ewing and Arthur Lindsey Egan, Johannesburg, Unionof South Africa Application April 6, 1934, Serial No. 719,400 the Unionof South Africa August 29, 1933 7 Claims.

The present invention relates to methods and apparatus for producingcompressed air in a highly devaporized condition. One of the uses towhich this product may be put is that of conditioning mine air byexpanding the devaporized compressed air against a load so as to produceexhaust air which is both dry and cold and using such exhaust air tocondition the mine air, as by mixing it with the latter.

m For supplying to a mine de-humidifled compressed air suitable forconditioning the mine air as described in the last paragraph, it hasbeen proposed to devaporize the air at the pressure of its delivery tothe mine and before such delivery.

According to the present invention, the air is first provided under theconditions (a) That it is over-compressed; i. e. it is at a pressuresubstantially higher than its working pressure. By working pressure ismeant the pressure at which it is required to be when devaporized andready for its intended use; for instance the pressure at which it is tobe delivered to a mine and to mine machinery.

, (b) That its temperature is about the prevailing temperature.

(0) That it is dry in the sense that moisture which has condensed byreason of its compression and cooling to the prevailing temperature hasbeen removed from it.

Such over-compressed air is cooled by heat exchange as explainedhereafter and is then expanded, in a motor driving a load, down to itsworking pressure. Thereby it is substantially cooled; itsover-compressed pressure and its heatexchange cooling being preferablyso arranged that its expansion down to its working pressure reduces itto the freezing temperature of water. The cooling by heat exchange andthe further cooling in the expansion motor causes condensation of watervapour which was present in the over-compressed air; and when freezingtemperature is attained as aforesaid practically the whole of the watervapour is condensed. The two condensates are removed from the air.

The cold and de-watered exhaust from the expansion motor at the workingpressure is then passed through the heat exchange step mentioned abovewhereby it cools the over-compressed air passing to the motor and isitself brought nearer to the prevailing temperature. The product thusconsists of air at working pressure, highly de-' vaporized, and readyfor its intended use.

The heat exchange between the over-com- 5 pressed air going to the motorand the com- Dressed air exhaustedfrom the motor is an important featureof the invention from the eco nomic aspect since it reduces thetemperature range through which the air must pass in the expansion motorin order to attain the final temperature corresponding to the desireddegree of devaporization. correspondingly with the temperature range,the necessary pressure range is reduced; and, as the flnal pressure isdetermined by the working pressure at which the air is to be delivered,the net result is to'minimize the degree of over-compression to whichthe air must initially be brought. The degree of overcompression is alsodependent upon the adiabatic efficiency of the expansion motor. 5

A further feature of the invention which is economically important isthat the work derived from the expansion motor is applied to assist thecompression of the air; v

The invention is illustrated in the accompanying drawings in which:

Figure I is a diagrammatic representation of apparatus for conditioningmine air.

Figure 11 is a similar representation of surface plant including apre-existing compressor.

Figure III shows a surface plant suitable for the case where compressedair is available from a public supplyat a pressure above the mineworking pressure. Referring to Figure I, 2 indicates a compressor whichtakes in atmospheric air at 3 and delivers it at 4 at a pressure higherthan that at which the air is required to be delivered to the minecompressed air system 5. Saidv compressor 2 would usually compress instages indicated by 6, I, 8, 9, I0. It may also cool the air betweensome stages, but in any event the delivered compressed air is cooled atH by natural means available for bringing it to about the prevailingtemperature. As shown it is cooled by water taken in at l2 and deliveredat 13 to say a cooling pond. The condensate is removed at it.

The cooled compressed air is passed, as indicated by arrow I5, through aheat exchanger it where it is further cooled. Moisture precipitated bysuch cooling is removed at ll. The cooled and de-watered air is suppliedto the expansion motor l8. Said motor is shown as driving the compressor2 and thereby assisting the main compressor motor is. In said expansionmotor I8 the air is expanded to its working pressure, that is thepressure at which it is to be delivered to the mine system 5.

In expanding in the motor la, the air falls to a low temperature.Preferably it is brought to the freezing temperature of water. Itsvapour content is thereby precipitated as water or ice, and is removedat 20. The cold dewatered exhaust air is led, as indicated by the arrow2i, 5 through the heat interchanger it where it cools theover-compressed air passing at l5 to said motor l8. From the heatinterchanger, the air, now at working pressure and highly devaporized iscon-- ducted to the mine compressed air system 6. It

is worked in expansion motors for various purposes as described in thespecification of our application No. 683,528; for instance in theexpansion motor 22 which drives the pump 23. When exhausted from saidmotor 22 it is discharged into the mine atmosphere at 24 or otherwiseemployed to condition the mine atmosphere.

Figure 11 shows a surface arrangement suitable for the case where thereexists a compressor 2a adapted to produce compressed air at the workingpressure. It is desirable in this case to provide the water cooler 25for cooling the air delivered by the compressor 2a; said cooler 25having means 26 for removing water condensed 25 by the cooling.Additional plant required includes the compressor Illa which is drivenby the expansion motor l8 and a make-up motor 21; together with thecooler i l and the heat exchanger l6 as in the last example. The airfrom the 30 compressor 20. is thus cooled at 25, dewatered at 26,over-compressed at Illa, again cooled at H,

dewatered at I, further cooled at i5, re-expand ed at l8 and dewateredat 20 with heat interchange at It between the air going to and aircoming from the expansion motor 20, and dewatering at H.

Figure III illustrates the case where air at a higher pressure than theworking pressure and at about the prevailing temperature, is delivered40 from a public supply at 28.

Such air is passed through the heat exchanger l6, dewatered at H, andthen conducted to the expansion motor l8. The latter drives anyappropriate load indicated by 29. The exhaust from the expansion motori8 is de-watered at. 20, passed through the heat exchanger l6 and thenceconveyed to the mine system 5.

We claim:

1. The process of conditioning mine air by providing, at the surface ofthe mine, air which is compressed to a higher pressure than the workingpressure at which it is to be used in said mine, said air being at theprevailing temperature and containing no water other than water vapour,cooling such air by heat exchange with the air exhausting from anexpansion motor, further cooling it by expanding it against a load insaid expansion motor down to its working pressure, causing the coldexhaust compressed air from said expansion motor to cool theover-compressed air incoming thereto, then working said air expansivelyin the second expansion motor driving a loadand causing it thereafterto'cool the mine atmosphere.

2. The process of conditioning mine air by compressing air at thesurface of the mine to a pressure substantially above its workingpressure in said mine, cooling it by a naturally occurring coolingmedium such as air or water to about the prevailing temperature,removing from it moisture condensed from such compression and cooling,cooling it by heat exchange with the air exhausting from an expansionmotor, further cooling it by expanding it against a load in saidexpansion 75 motor down to its working pressure, causing the coldexhaust compressed air from said expansion motor to cool theover-compressed air incoming to said expansion motor, thereafter workingsaid air expansively in a. second expansion motor driving a load andthen causing it to cool the mine 6 atmosphere.

3. The process which consists in providing air at about the prevailingtemperature and contain ing no water other than water vapour and at apressure substantially above a predetermined 10- working pressure sothat when it has been cooled, expanded and warmed as hereafterspecified, it will attain said working pressure and be at about theprevailing temperature, cooling such air by heat exchange with the airexhausting from an 15 expansion motor, removing resulting condensate,further cooling it by expanding it in said expansion motor and against aload until it reaches said predetermined pressure, removing resultingcondensate, then causing the cold compressed air ex- 20 hausted fromsaid motor to cool the over-compressed air which isentering said motor,and thereby warm itself to about the prevailing temperature, soproviding a supply of compressed air which, by reason of its being atthe working pres- 25 sure and about the prevailing temperature, isavailable as a source of power and is highly devaporized.

4. The process which consists in compressing air to a pressuresubstantially above a predetermined working pressure so that when it hasbeen cooled, expanded and warmed as hereafter specified it will attainsaid working pressure and be about the prevailing temperature, coolingthe whole of the so compressed air by a cooling medium to about theprevailing temperature, removing resulting condensate, cooling it byheat exchange with the air exhausting from an expansion motor, removingresulting condensate,

further cooling it by expanding it in said expansion motor and against aload until it reaches said predetermined pressure, removing resultantcondensate, then causing the cold compressed air exhausted from saidmotor to cool the over-compressed air which is entering said motor, and45 thereby warm itself to about the prevailing tem-' terature, soproviding a supply of compressed air which, by reason of its being atthe working pressure and about the prevailing temperature, is availableas a source of power and is highly devaporized.

5. The process which consists in providing air at about the prevailingtemperature and containing no water other than water vapour and at apressure substantially above a predetermined 55 working pressure so thatwhen it has been cooled, expanded and warmed as hereafter specified, itwill attain said working pressure and be at about the prevailingtemperature, cooling such air by 56} heat exchange with the airexhausting from an expansion motor, removing resulting condensate,further cooling it by expanding it in said expansion motor and against aload until it reaches said predetermined pressure, and is, at a tem- 65perature not higher than the freezing temperature of water, removingresulting condensate, then causing the cold compressed air exhaustedfrom said motor to cool the over-compressed air which is entering saidmotor, and thereby warm itself to about the prevailing temperature, soproviding a supply of compressed air which, by reason of its being atthe working pressure, and about the prevailing temperature, is availableas a source of power and is highly devaporized.

6. The process which consists in compressing air to a pressuresubstantially above a predetermined working pressure so that when it hasbeen cooled, expanded and warmed as hereafter specified it will attainsaid working pressure and be at about the prevailing temperature,cooling the whole of these compressed air by a cooling medium to aboutthe prevailing temperature, removing resulting condensate, cooling it byheat exchange with the air exhausting from an expansion motor, removingresulting condensate, further cooling it by expanding it in saidexpansion motor and against a load until it reaches said predeterminedpressure, removing resultant condensate, causing the energy given out bysaid expansion motor to assist in compressing the air as aforesaid tothe pressure substantially above its working pressure, then causing thecold compressed air exhausted from said motor to cool theover-compressed air which is entering said motor, and thereby warmitself to about the prevailing temperature, so providing a supply ofcompressed aid which, by reason of its being at the working pressure andabout the prevailing temperature. is available as a source oi power andis highly devaporlaed.

7. Apparatus for producing highly devaporiaed air having a substantialenergy content due to its pressure, comprising a source oirelativelyhighly compressed air, a heat interchanger having means forconducting the original compressed air through it so that said air iscooled, means for removing condensate from said air, an expansion motorarranged to receive the relatively highly compressed air and having sucha ratio oi expansion as to exhaust it at a pressure substantially aboveatmospheric pressure and at a temperature of substantially the freezingpoint of water, a load for the expansion motor, means for removingcondensate from the motor exhaust air, and means to conduct thedevaporized exhaust air through the heat intercharger, the heatinter-changer providing such rate of heat exchange that said exhaust airis warmed by the original compressed air to about the prevailingtemperature.

SYDNEY EDWARD TRACKER EWING. ARTHUR LINDSEY EGAN.

